Method of forming self-assembled patterns using block copolymers, and articles thereof

ABSTRACT

A method of forming a block copolymer pattern comprises providing a substrate comprising a topographic pre-pattern comprising a ridge surface separated by a height, h, greater than 0 nanometers from a trench surface; disposing a block copolymer comprising two or more block components on the topographic pre-pattern to form a layer having a thickness of more than 0 nanometers over the ridge surface and the trench surface; and annealing the layer to form a block copolymer pattern having a periodicity of the topographic pre-pattern, the block copolymer pattern comprising microdomains of self-assembled block copolymer disposed on the ridge surface and the trench surface, wherein the microdomains disposed on the ridge surface have a different orientation compared to the microdomains disposed on the trench surface.

BACKGROUND

The present disclosure is related to a method of forming patterns ofsub-optical lithographic dimensions using self-assembly of blockcopolymers, and articles thereof.

Block copolymers, consisting of two or more distinct homopolymers joinedend to end, self-assemble into periodic microdomains having typicaldimensions of 10 nanometers to 50 nanometers (nm). The possibility ofusing such microdomains to pattern surfaces has attracted increasinginterest because of the expense and difficulty of patterning innanoscale dimensions (especially sub-45 nm) using optical lithography.

Controlling the lateral placement of the block copolymer microdomains onthe substrates continues to be a challenge. This problem has beenpreviously addressed using lithographically pre-defined topographicand/or chemical patterning of the substrate. Previous studies havedemonstrated that self-assembled block copolymer microdomains in form oflamellae can be directed to follow chemical patterning of the substrate,yielding periodicities close to those of the chemical pre-patterns.Other studies have shown that by controlling the surface wettingproperties of the block copolymer on the bottom and side walls of atopographic pre-pattern, the lamellae can be directed to follow thetopographic pre-pattern. The lamellae formed line/space patterns ofsmaller dimensions than the substrate pre-pattern, subdividing thetopographic pre-pattern into a higher frequency line pattern; that is, aline pattern having a smaller pitch. One limitation of block copolymerpatterning is the propensity of the patterns to form everywhere on thepre-pattern surface, for topographic and/or chemical guidingpre-patterns.

Thus, new methods are desired for forming self-assembled block copolymernanopatterns having controlled lateral placement of the microdomains onthe substrate.

BRIEF SUMMARY

A method of forming a block copolymer pattern comprises providing asubstrate comprising a topographic pre-pattern comprising a ridgesurface separated by a height, h, greater than 0 nanometers from atrench surface; disposing a block copolymer comprising two or more blockcomponents on the topographic pre-pattern to form a layer having athickness of more than 0 nanometers over the ridge surface and thetrench surface; and annealing the layer to form a block copolymerpattern having a periodicity of the topographic pre-pattern, the blockcopolymer pattern comprising microdomains of self-assembled blockcopolymer disposed on the ridge surface and the trench surface, whereinthe microdomains disposed on the ridge surface have a differentorientation compared to the microdomains disposed on the trench surface.

A semiconductor device comprises a substrate, the substrate comprising atopographic pre-pattern comprising a ridge surface separated by aheight, h, greater than 0 nanometers from a trench surface; and a layercomprising a block copolymer disposed on the substrate, the blockcopolymer comprising two or more block components, and the layer havinga thickness of more than 0 nanometers over the ridge surface and thetrench surface; wherein the layer comprises a block copolymer patternhaving a periodicity of the topographic pre-pattern, the block copolymerpattern comprising microdomains of self-assembled block copolymerdisposed on the ridge surface and the trench surface, wherein themicrodomains disposed on the ridge surface have a different orientationcompared to the microdomains disposed on the trench surface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic representation of the pattern formation resultingfrom the disclosed method. The height, h, of the surface feature isabout L_(o)/2 of lamellar periodicity of block copolymer. The thickness,t′, of block copolymer on top of the ridge surface is L_(o) forasymmetric wetting block copolymers, and L_(o)/2 for symmetric wettingblock copolymers.

FIG. 2 is a plan view scanning electron micrograph (SEM) image oflamellar morphology on a topographic pre-pattern having 100 nm pitch.The variation of film thickness of PS-b-PMMA [poly(styrene-block-methylmethacrylate)) on the pre-pattern controlled the discrete line patternformed.

FIG. 3, like FIG. 2, is a plan view scanning electron micrograph (SEM)image of lamellar morphology on a topographic pre-pattern, except thepre-pattern has a 150 nm pitch. The block copolymer patterns of FIG. 2and FIG. 3 replicate the pitch of the underlying pre-pattern.

FIG. 4 is a plan view SEM image of a partially coated film. The lamellarmicrodomains locate on top of the ridge surfaces of the underlyingpre-pattern.

FIG. 5 is a plan view SEM image of the lamellar microdomains at the endof underlying pre-pattern lines. The ridge surface effectively controlsthe starting points of the block copolymer pattern.

FIG. 6 is a set of plan view SEM images of the block copolymermicrodomains formed on top of topographic pre-patterns having a varietyof geometric shapes. The pre-pattern line segments making up the sidesof each shape do not intersect. Each geometric shape has two sizes.

FIG. 7 is a schematic 3-dimensional representation of the orientation oftwo adjacent lamellar microdomains formed on a ridge surface using anA-B block copolymer, and the arrangement of the A blocks and the Bblocks to form the A and B microdomains.

The disclosure may be understood more readily by reference to thefollowing detailed description of the various features of the disclosureand the examples included therein.

DETAILED DESCRIPTION

Disclosed is a method for controlling lateral placement of sub-opticalpatterns formed by block copolymer thin films. The method producesdiscrete patterns by means of topographically directed self-assembly ofthe block copolymer. Thus, the formation of the block copolymer patternis controlled by the block copolymer film thickness, and the lateralplacement of the block copolymer pattern is controlled by the substratesurface topography. Thus, the block copolymer patterns replicate thespacing, or periodicity, of the underlying topographic pre-pattern ofthe substrate. The method does not rely on chemical modification of thesubstrate. The method makes it possible to generate new types oflamellar patterns having controlled placement of the block copolymerpattern on a topographic pre-pattern. Unlike other directedself-assembly methods of block copolymers that provide patternscontinuously covering the substrates, the disclosed method provides newtypes of discrete patterns that can be formed on selected portions of asubstrate, which can be directly applicable to device fabrications.

The substrate can comprise one or more layers. The topmost layer has asurface comprising a topographic pre-pattern, such as for example alithographic line pattern. The topographic pre-pattern has at least onesurface feature comprising a ridge surface separated by a height, h,greater than 0 nanometers from a lower lying trench surface. The ridgesurface comprises at least one ridge surface area having a preferentialaffinity for one of the block components of the block copolymer.

The block copolymer comprises two or more polymeric block components.The block components are derived from different chemical monomers. Forexample, a block copolymer can comprise a polystyrene block component(A) and a poly(alkyl(meth)acrylate) block (B), represented by theformula (A-b-B)_(x), wherein each block can have a different numberaverage molecular weight, and wherein the poly(alkyl(meth)acrylate)block can be derived from either an acrylate or a methacrylate monomer.More specifically, block component (B) can be poly(methyl methacrylate).No limitation is placed on the number of the A-B diblock sequences inthe block copolymer; that is, x in the formula (A-b-B)_(x) is an integergreater than or equal to 1. In one embodiment, the block copolymerconsists essentially of, or exclusively of two block components, and xis 1.

The block copolymer is disposed in the form of a film layer on thesubstrate topographic pre-pattern. The layer has a thickness, t′, overthe ridge surface and a thickness, t, over the trench surface, where t′and t are each greater than 0 nanometers and t′ is less than t.Annealing the layer results in a block copolymer pattern having aperiodicity of the topographic pre-pattern. The block copolymer patternis comprised of microdomains of self-assembled block copolymer disposedon the ridge surface and the trench surface, wherein a microdomaindisposed on the ridge surface has a different orientation compared to amicrodomain disposed on the trench surface. The difference inorientation is detectable on a macro-scale as the block copolymerpattern. Herein, the term “block copolymer pattern” refers to a patternresulting from the ordered assembly of microdomains based on theirorientation relative to the underlying surface. The block copolymerpattern periodicity is a macro-scale periodicity controlled by theunderlying topographic pre-pattern and therefore replicates theperiodicity of the underlying topographic pre-pattern. The blockcopolymer pattern periodicity is distinguished from lamellarperiodicity, described below. Lamellar periodicity is a micro-scaleperiodicity derived from the ordered self-assembly of block copolymermolecules, and is controlled by the block copolymer structure, not theunderlying topographic pre-pattern.

More specifically, annealing the block copolymer layer causes the blockcopolymer to self-assemble into lamellar microdomains disposed on theridge surface and the trench surface. The lamellar microdomains can haveeither a parallel or perpendicular orientation relative to theunderlying pre-pattern surface plane; that is, the lamellar “plane” canbe parallel or perpendicular to the underlying surface plane. Thelamellae that form over the trench surface are substantially orientedparallel to the underlying trench surface plane, whereas the lamellaethat form over the ridge surface are substantially orientedperpendicular to the underlying ridge surface plane. The difference inplanar orientation of the lamellae can be detected as a block copolymerpattern by SEM when viewed from above the pre-pattern surface plane. Inthe SEM, the lamellae having a parallel orientation relative to theunderlying surface plane appear free of structure, while lamellae havingperpendicular orientation show structured contrast regions.

The lamellar microdomains disposed on the ridge surfaces having aperpendicular orientation can extend partially over the trench surfacearea. Further, the lamellar microdomains having a perpendicularorientation may also be substantially or exclusively located on theridge surface.

Hereinafter the pre-patterned topographic surface of the substrate willbe referred to simply as the “pre-pattern”.

No limitation is placed on the configuration of the underlyingpre-pattern or the pattern formed by the block copolymer coated thereon,with the proviso that the desirable block copolymer properties are notadversely affected; for example, the self-assembly of the blockcomponents to form microdomains on ridge surfaces during annealing, orthe formation of detectably different microdomain orientations on theridge surface. The pre-pattern can comprise surface features in the formof different geometric shapes; for example parallel lines, grids,polygons, concentric circles, arcs, curvilinear shapes, open angles, orcombinations thereof. The block copolymer pattern replicates theperiodicity of the underlying pre-pattern, and therefore the blockcopolymer pattern can also comprise parallel lines, grids, polygons,circles, arcs, curvilinear shapes, open angles, or combinations thereof,having a size and shape corresponding to the underlying pre-pattern.

FIG. 1 is a schematic cross-sectional view of a non-limiting example ofa substrate 10 comprising a pre-pattern having a block copolymer layer12 disposed thereon, wherein the view is a close-up of a surface feature20 of the underlying pre-pattern. Surface 22 of the block copolymerlayer 12 is in contact with the air. Surface feature 20 has width, w,and comprises sidewall 14 and ridge 16 having ridge surface 18, adjacentto trench 20 comprising trench surface 24. Ridge surface 18 is displacedabove trench surface 24 by a height, h. The block copolymer layer 12 isa non-conformal layer, meaning that it varies in thickness with thesurface features of the underlying pre-pattern as shown in FIG. 1. Thus,the thickness, t, of block copolymer layer 12 above trench surface area24 is greater than thickness, t′, of the block copolymer layer 12 overridge surface area 18. The substrate can comprise additional layers (notshown), the topmost layer which comprises the pre-pattern.

The term “annealing” or “anneal” as used herein refers to treatment ofthe block copolymer so as to allow sufficient phase separation betweentwo or more different block components of the block copolymer to promoteself-assembly of the block components into an ordered pattern havingrepeating structural units. Annealing of the block copolymer can beachieved by various methods known in the art, including, but not limitedto: thermal annealing (either in a vacuum or in an inert atmospherecontaining nitrogen or argon), ultra-violet annealing, laser annealing,solvent vapor-assisted annealing (either at or above room temperature),or supercritical fluid-assisted annealing. As a specific example,thermal annealing of the block copolymer can be conducted at an elevatedtemperature that is above the glass transition temperature (Tg), butbelow the degradation temperature (Td) of the block copolymer.

The wetting properties as discussed herein refer to the surfaceaffinities of a specific surface with respect to the different blockcomponents of the block copolymer. For example, if a surface hassubstantially the same surface affinity to both block components A and Bof a block copolymer, such a surface is considered a neutral surface ora non-preferential surface, i.e., both block components A and B can wetor have affinities to such a surface. In contrast, if a surface hassignificantly different surface affinities for the block components Aand B, such a surface is then considered a preferential surface, i.e.,only one of block components A and B can wet such a surface, but theother cannot.

A symmetric wetting block copolymer is defined as one that when coatedon a surface and annealed will self-assemble to place block componentsof the same chemical composition in contact with the pre-pattern surfaceand air interface. For example, an A-B diblock copolymer would besymmetrically wetting if it self-assembles to place the A block incontact with the pre-pattern surface and the air interface; likewise ifit self-assembles to place the B block in contact with the pre-patternsurface and air interfaces.

An asymmetric wetting block copolymer is defined as one that when coatedon a pre-pattern surface and annealed, will self-assemble to placecopolymer blocks having different chemical compositions in contact withthe pre-pattern surface and the air interface. For example, A-B diblockcopolymer would be asymmetrically wetting if it self-assembled to placethe A block in contact with the pre-pattern surface and the B block incontact with the air interface, or if the B block was in contact withthe pre-pattern surface and the A block was in contact with the airinterface.

In another more explicit example of symmetric wetting, ifpoly(styrene-block-methyl methacrylate) (PS-b-PMMA, a diblock copolymer)is coated onto a hydrophobic surface and annealed, the (PS) blockarranges to be in contact with the hydrophobic surface, followed bypoly(methyl methacrylate) (PMMA), PMMA, and PS blocks sequentiallystacked thereon. The upper and outermost PS block has a low surfaceenergy and preferentially arranges to be in contact with the airinterface. This is symmetric wetting because PS blocks are in contactwith the hydrophobic surface and the air interface.

In a more explicit example of asymmetric wetting, if PS-b-PMMA is coatedon a hydrophilic surface and thermally treated, the first block incontact with the hydrophilic surface will be the PMMA block, followedsequentially by PS, PS, PMMA, PMMA, and PS blocks stacked thereon, withPS at the air interface. This is asymmetric wetting because the PMMAblock contacts the hydrophilic surface and a PS block contacts the airinterface.

L₀ refers to the natural periodicity of the block copolymer, or thelength of the repeating structural unit of the self-assembled blockcopolymer. More generally, in a diblock copolymer A-B, the structuralrepeat unit is A-B in a stacked structure. In a triblock copolymerA-B-C, the structural repeat unit is A-B-C. In the above example of A-Bdiblock copolymer, the A-B polymer chains self-assemble in an A-B B-AA-B sequential pattern. L₀ consists of two lamellar domains, onelamellar domain consisting of the two adjacent B blocks and anotherlamellar domain consisting of the two adjacent A blocks. This shown alsoin FIG. 7, described below. The length, L₀, can be calculated from thenumber average molecular weight (or degree of polymerization, N) of eachblock in the block copolymer.

Continuing with the non-limiting example of a diblock copolymer, when atopographic pre-pattern that has been coated with a film of the diblockcopolymer is annealed at a high temperature, typically above the glasstransition temperature, T_(g), of the diblock copolymer, a molecularrearrangement can occur in the layer to form a stacked assembly ofcopolymer blocks. In symmetric wetting cases, a quantized blockcopolymer thickness of nL₀ is obtained. In asymmetric wetting cases, aquantized block copolymer thickness of (n+½)L₀ is obtained. In eachcase, n is an integer greater than zero. In a region where the initialthickness is thinner than a quantized thickness after the thermaltreatment, a hole is formed. In a region where the initial thickness isthicker than a quantized thickness after the thermal treatment, anisland is formed. In the disclosed method, the thickness variation ofthe block copolymer film becomes L₀ by self-assembly upon annealing.

More specifically, referring again to FIG. 1, for asymmetric wettingblock copolymers the thickness, t′, is equal to or about equal to L₀.For symmetric wetting block copolymers the thickness, t′, is equal to orabout equal to L₀/2. Further, in the disclosed method, the ridge surfacearea has a height, h, of L₀/2 for both asymmetric and symmetric wettingblock copolymers. The area of the ridge surface having height, h, ofL₀/2 above the trench area can be more than 0% to 100%, morespecifically about 20% to about 100%, even more specifically about 40%to about 100%, still more specifically about 60% to about 100%, or evenmore specifically about 80% to about 100% of the total area of the ridgesurface. The ratio between the ridge surface area and trench surfacearea (referred to as the duty cycle) can be any non-zero positive value.That is, as long as there is a ridge surface area, the lamellar blockcopolymer pattern can be formed, as demonstrated by the various patternsin FIG. 6. The width, w, of the ridge surface area (FIG. 1) can be apositive value from greater than 0 to less than 2L₀.

The substrate surface on which the block copolymer is disposed cancomprise inorganic or organic materials such as metals, carbon, orpolymers (photoresists). More particularly, the substrate surface onwhich the block copolymer is disposed can comprise any semiconductingmaterial including, for example, Si, SiGe, SiGeC, SiC, Ge alloys, GaAs,InAs, InP, as well as other III-V or II-VI compound semiconductors. Thesubstrate surface may also comprise a layered semiconductor such asSi/SiGe, or a semiconductor-on-insulator (SOI). In particular, thesubstrate surface is composed of a Si-containing semiconductor material,i.e., a semiconductor material that includes Si. The semiconductormaterial may be doped, undoped or contain both doped and undoped regionstherein. Substrate surfaces comprising one of silicon native oxides,silicon oxides, and silicon nitrides are preferentially wetted by, forexample, PMMA block components, but not by PS block components of aPS-b-PMMA block copolymer. Therefore, such surfaces can be used aspreferential surfaces for PS-b-PMMA block copolymers.

In the following discussion of FIG. 2-6, materials and methods used toobtain the SEM images can be found in the EXAMPLE at the end of theDetailed Description section.

Annealing the block copolymer layer induces self-assembly of blockcopolymer to form perpendicularly oriented lamellar microdomainsrelative to the ridge surface plane. The lamellar microdomains disposedon the ridge surface form a detectable line pattern that can have awidth greater than w (FIG. 1) of the ridge surface. This is illustratedin the composite images of FIG. 2 and FIG. 3, for two substrates whosesub-optical topographic pre-patterns comprise differently spaced lines.The dimensions of the surface features making up four of the pre-patternlines are shown in top portion 30 of FIG. 2, and in top portion 40 ofFIG. 3. The pre-pattern lines of FIG. 2 have a pitch, p, of 100nanometers (nm) and a ridge width, w, of 25 nm. The pre-pattern lines inFIG. 3 have a pitch, p, of 150 nm and a ridge width, w, of 27 nm. Thebottom SEM image 32 in FIG. 2 and the bottom SEM image 42, of FIG. 3 areplan view scanning electron micrographs (SEM) of each pre-pattern aftercoating a layer of polystyrene-poly(methyl methacrylate) block copolymer(PS-b-PMMA) thereon, and annealing the resulting film by thermaltreatment to induce self-assembly of block copolymer, that results inthe formation of the perpendicularly oriented lamellar microdomains 34and 44 in FIG. 2 and FIG. 3 respectively. The perpendicularly orientedlamellae form over the ridge surfaces of the underlying pre-patterns,demonstrating that the lamellar orientation relative to the underlyingsurface plane is controlled by the thickness of the block copolymerlayer.

The block copolymer patterns in FIG. 2 and FIG. 3 each have twoadditional levels of order, long range order along the long axis of thepre-pattern surface feature (in this example, lines), and short rangeorder normal to the long axis of the pre-pattern surface feature. Theshort range order is seen in the SEMs as a discontinuous stitch-likepatterns across the long axis of the ridge surface. Each “stitch” is aperpendicularly oriented lamellar microdomain. The lamellar plane isalso aligned transversely with respect to the long axis of theunderlying pre-pattern line. The dark and bright regions in the stitchescorrespond to the PMMA and PS phases, respectively. The in-lens detectorof the SEM detects different amounts of backscattered electrons from thePMMA and PS blocks, producing the observed contrast. In these twoexamples, the PMMA and PS block phases are aligned perpendicular to thelamellar plane, and parallel to the ridge surface plane. This is shownschematically in FIG. 7. In FIG. 7, the planes containing the twolamellar microdomains 100 are oriented perpendicular to the planecontaining the ridge surface 104. The lamellar microdomains 100 are alsooriented transversely to the long axis of the ridge surface, representedby the arrow 106. The arrangement of block component phases A and Bwithin each lamellar microdomain 100 are also shown, where the stackingsequence is A-B B-A A-B. One lamellar microdomain 100 contains twosequential A blocks (labeled A domain), the other lamellar microdomain100 contains two sequential B blocks (labeled B domain) of the A-B blockcopolymer. Also shown is L₀ which comprises the two lamellarmicrodomains 100. A polymer chain within the A and B domain phases canbe in the form of a random coil, mesogen, helix, or a combination of theforegoing forms.

The long range order of the block copolymer pattern derives from amultitude of perpendicularly oriented lamellar microdomains (stitches),arranged along the long axis of a ridge surface as shown in FIG. 7. In afurther embodiment, the perpendicularly oriented lamellar plane can alsobe aligned parallel to the long axis of the underlying pre-pattern line.

Thus, the lamellar microdomains whose lamellar planes are orientedperpendicular to the underlying surface plane appear as alternatingpatterns of light and dark gray in the SEMs of FIG. 2 and FIG. 3, andare located over the ridge surfaces of the underlying pre-pattern. Thetrench areas between the substrate pre-pattern lines appear dark gray,having no observable structure in the SEM due to the parallelorientation of lamellar plane relative to the plane containing thetrench surface. The block copolymer pattern is also a line pattern andhas a width of approximately 65 nm in each of the SEM images of FIGS. 2and 3. This line width is approximately 2.5 times the width, w, of theunderlying pre-pattern line. As shown, the pitch of the underlyingpre-pattern lines is reproduced in the block copolymer patterns of FIG.2 and FIG. 3. Thus, the block copolymer pattern has a line spacing ofabout 100 nm in FIG. 2, and about 150 nm in FIG. 3, corresponding to thepitch of the underlying pre-pattern. FIG. 2 and FIG. 3 illustratepre-patterns having a constant line pitch. In an embodiment, thepre-pattern can also have a varying pitch.

FIG. 4 is a plan view SEM image of a pre-pattern whose ridge surfacesare also in the form of a set of parallel lines. The pre-pattern waspartially coated with PS-b-PMMA and annealed by thermal treatment.Uncoated pre-pattern ridge surfaces 52 and uncoated trench surfaces 54have lighter shades of gray in the SEM. The coating boundary isindicated generally at 56, wherein the block copolymer layer thicknessgradually increases to a thickness suitable for formation ofperpendicularly oriented lamellar microdomains 58 over the coated ridgesurfaces, but not over the coated trench areas 60.

FIG. 5 is a plan view SEM of a pre-pattern consisting of parallel linesthat end at the point of the indicated dashed line 70. Area 72 has noridge surfaces and is all trench (flat). The entire surface area of thepre-pattern has been coated with block copolymer, followed by thermalannealing to induce block copolymer self-assembly. The SEM of FIG. 5demonstrates that the perpendicularly oriented lamellar microdomains 74end at a point near the end of the underlying pre-pattern lines. Thisprovides additional evidence that the perpendicularly oriented lamellarmicrodomains are centered over the ridge surfaces of the pre-patternlines, and also that the pre-pattern ridge surfaces control the lateralplacement of the perpendicularly oriented lamellar microdomains.

The length of the pre-pattern lines determines the number ofperpendicularly oriented lamellar microdomains (“stitches”) that canform on a ridge surface. This is demonstrated in FIG. 6, a compositeimage illustrating block copolymer patterns formed using a variety ofgeometric pre-patterns composed of 1 to 6 line segments (e.g., linesegment, parallel line segments, triangle, square, pentagon, andhexagon). The top row of images indicated as 80 schematically shows thepre-pattern geometric figure used to generate the block copolymerpatterns in the SEMs directly below each geometric figure. The middlerow SEM images, 82, and bottom row SEM images, 84, compare differentsizes of the geometric pre-patterns comprising different length linesegments. In each case, the pre-pattern line segments 86 making up thegeometric figures do not intersect. As seen in the SEMs, the middle row82, having longer line segments per edge, produces 3 perpendicularlyoriented lamellae per line segment, indicated as 88. The bottom row 84having shorter line segments per edge in the pre-pattern produces 2perpendicularly oriented lamellae per line segment, indicated as 90. Ineach case, the stitches comprising lamellar microdomains are alignedtransversely to the long axis of the underlying pre-pattern linesegment. In some cases, the stitches align at an angle other thantransversely to the long axis of the underlying pre-pattern line. Thiscan occur in particular when the lamellar microdomains are located nearthe ends of a pre-pattern line, or when located over defects in theunderlying pre-pattern lines.

The term “defect” or “defects” as used herein refers to any unwanteddiscontinuity in the translational, orientational, or chemicalcompositional order of a pattern. For example, a defect can be anunwanted notch, crack, bulge, bend or other physical discontinuity inthe surface feature of the pre-pattern, or a chemical compositionalchange in a surface area of a pre-pattern. In another example, when theblock copolymer pattern is defined by alternating lamellae, it may bedesirable that the lamellae in such a block copolymer pattern must bealigned along the same direction in order for the pattern to beconsidered defect-free. Defects in the lamellar patterns can havevarious forms, including dislocation (i.e., line defects arising fromperturbations in the translational order), disclination (i.e., linedefects arising from discontinuities in the orientational order), andthe like. Although it is generally desirable to minimize defects, norestriction is placed on the number of defects per unit area in thepre-pattern or block copolymer pattern formed thereon.

There are many different types of block copolymers that can be used forforming the self-assembled block copolymer patterns. As long as a blockcopolymer contains two or more different polymeric block componentshaving different surface affinities for the ridge surface areas, suchtwo or more different polymeric block components are capable ofself-assembling into microdomains having nano-sized structural units.

In an embodiment, the block copolymer consists essentially of a firstpolymeric block component A and a second polymeric block component Bthat are immiscible with each other. By immiscible is meant thathomopolymers of each block component form a melt blend exhibitingmultiple glass transition temperatures representing each homopolymerphase. Additionally, one of the components A and B is selectivelyremovable without having to remove the other, so as to form eitherisolated and orderly arranged structural units composed of theun-removed component, or a continuous structural layer containingisolated and orderly arranged cavities formed after the removablecomponent has been removed. Alternatively, the components A and B maysimply have different electrical, optical, and/or magnetic properties,so that the ordered patterns composed of such components A and B can beused for fabricating different device structures.

With two chemically distinct blocks A and B, the block copolymer maycontain any numbers of the polymeric block components A and B arrangedin any manner. The block copolymer can have a linear or branchedstructure. For example, the block copolymer may have any one of thefollowing formula:

More specifically, the block polymer is a linear diblock copolymerhaving the general formula of A-B. Specific examples of block copolymersthat may be used for forming the self-assembled block copolymer patternsinclude, but are not limited to: polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA), poly(ethylene oxide)-block-polyisoprene(PEO-b-PI), poly(ethylene oxide)-block-polybutadiene (PEO-b-PBD),poly(ethylene oxide)-block-polystyrene (PEO-b-PS), poly(ethyleneoxide)-block-poly(methyl methacrylate) (PEO-b-PMMA), poly(ethyleneoxide)-block-poly(ethyl ethylene) (PEO-b-PEE),polystyrene-block-poly(vinyl pyridine) (PS-b-PVP),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-poly(ferrocenyl dimethylsilane) (PS-b-PFS),polybutadiene-block-poly(vinylpyridine) (PBD-b-PVP), andpolyisoprene-block-poly(methyl methacrylate) (PI-b-PMMA).

The types of self-assembled microdomains formed by the block copolymerare readily determined by the volume fraction of the first blockcomponent A to the second block components B.

Specifically, when the volume ratio of the first block component A tothe second block component B is greater than about 80:20, the blockcopolymer will form an ordered array of spheres.

When the volume ratio of the first block component A to the second blockcomponent B is less than about 80:20 but greater than about 65:35, theblock copolymer will form an ordered array of cylinders composed of thesecond polymeric block component B in a matrix composed of the firstpolymeric block component A.

When the volume ratio of the first block component A to the second blockcomponent B is less than about 65:35 but is greater than about 35:65,the block copolymer will form alternating lamellae composed of the firstand second polymeric block components A and B.

When the volume ratio of the first block component A to the second blockcomponent B is less than about 35:65 but greater than about 20:80, theblock copolymer will form an ordered array of cylinders composed of thefirst polymeric block component A in a matrix composed of the secondpolymeric block component B.

When the volume ratio of the first block component A to the second blockcomponent B is less than about 20:80, the block copolymer will form anordered array of spheres composed of the first polymeric block componentA in a matrix composed of the second polymeric block component B.

Therefore, the volume ratio of the first block component A to the secondblock component B can be readily adjusted in the block copolymer inorder to form desired self-assembled periodic patterns.

In a particular embodiment, the block copolymer used for forming theself-assembled periodic patterns is PS-b-PMMA. PS and the PMMA blocks insuch a PS-b-PMMA block copolymer can each have a number averagemolecular weight ranging from about 10 kg/mol to about 100 kg/mol, witha number average molecular weight from about 20 kg/mol to about 50kg/mole being more typical.

The surface energies of PS and PMMA have been reported to be γ_(PS)=40.7dyn/cm and γ_(PMMA)=410.1 dyn/cm at 20° C. respectively. Water contactangles for polystyrene range around 84-91°, whereas for PMMA they arearound 75°.

Typically, mutual repulsion between different polymeric block componentsin a block copolymer is characterized by the term χN, where χ is theFlory-Huggins interaction parameter and N is the degree ofpolymerization. The higher χN, the higher the repulsion between thedifferent blocks in the block copolymer, and the more likely the phaseseparation therebetween. When χN is much greater than 10 (referred toherein as the strong segregation limit), there is a strong tendency forthe phase separation to occur between different blocks in the blockcopolymer.

For a PS-b-PMMA diblock copolymer, X can be calculated as approximately0.028+3.9/T, where T is the absolute temperature. Therefore, X isapproximately 0.0362 at 473° K (199.85° C.). When the number averagemolecular weight (M_(n)) of the PS-b-PMMA diblock copolymer isapproximately 51 Kg/mol, with a molecular weight ratio (PS:PMMA) ofapproximately 50:50, the degree of polymerization N is about 500, so χNis approximately 18.1 at 200° C. Alternatively, when M_(n) of thePS-b-PMMA diblock copolymer is approximately 64 Kg/mol, with a numberaverage molecular weight ratio (PS:PMMA) of approximately 66:34, thedegree of polymerization N is about 622.9, so χN is approximately 22.5at 200° C.

Therefore, by adjusting one or more parameters such as the composition,the total number average molecular weight, and the annealingtemperature, the mutual repulsion between the different block componentsin the block copolymer of the present invention can be readilycontrolled to effectuate desired phase separation between the differentblock components. The phase separation in turn leads to formation ofself-assembled periodic patterns, which comprise repeating structuralunits, for example spheres and cylinders, composed of different blockcomponents, as described hereinabove. More specifically, theself-assembling block copolymer forms lamellar repeating structuralunits when annealed. In another embodiment, the block copolymer does notself-assemble to form microdomains comprised of spheres or cylinders.

The periodicity or the dimension (L₀) of the repeating structural unitsin the periodic pattern is determined by intrinsic polymeric propertiessuch as the degree of polymerization N and the Flory-Huggins interactionparameter χ. At the strong segregation limit, L₀ is approximately equalto N^(2/3)χ^(1/6). In other words, L₀ scales with the degree ofpolymerization N, which in turn correlates with the number averagemolecular weight M_(n) and the number average molecular weight ratiobetween different polymeric block components. Therefore, by adjustingthe composition and the total number average molecular weight of theblock copolymer of the present invention, the dimensions of therepeating structural units can be readily tuned.

In order to form the self-assembled periodic patterns, the blockcopolymer can be first dissolved in a suitable solvent system to form ablock copolymer solution, which can then be applied onto the pre-patternto form a thin block-copolymer layer disposed thereon. Annealing thethin block-copolymer layer effectuates self-assembly between differentpolymeric block components contained in the block copolymer.

The solvent system for dissolving the block copolymer and forming theblock copolymer solution may comprise any suitable solvent, including,but not limited to toluene, propylene glycol monomethyl ether acetate(PGMEA), propylene glycol monomethyl ether (PGME), and acetone. Theblock copolymer solution may contain the block copolymer at aconcentration ranging from about 0.1 weight percent (wt %) to about 5 wt% based on total weight of the solution. More particularly, the blockcopolymer solution contains the block copolymer at a concentrationranging from about 0.5 wt % to about 1.5 wt %. In an embodiment, theblock copolymer solution comprises about 0.5 wt % to about 1.5 wt %PS-b-PMMA dissolved in toluene or PGMEA.

The block copolymer solution can be applied to the pre-pattern by anysuitable technique, including, but not limited to: spin casting,coating, spraying, ink coating, dip coating, and the like. Moreparticularly, the block copolymer solution is spin cast onto thepre-pattern, followed by solvent removal, leaving a thin film of blockcopolymer disposed on the pre-pattern.

The entire substrate is annealed to effectuate self-assembly of theblock copolymer. In particular, the block copolymer layer is thermallyannealed at a temperature that is above the glass transition temperature(T_(g)) of the block copolymer but below the decomposition ordegradation temperature (T_(d)) of the block copolymer. The thermalannealing step can be carried out at an annealing temperature of about200° C. to about 300° C. The thermal annealing can be performed for aperiod of more than 0 hours to about 100 hours, and more particularlyfor about 1 hour to about 15 hours. The thermally annealed blockcopolymer self-assembles to form lamellar microdomains whose planarorientation is perpendicular to the underlying surface plane over theridge surfaces of the underlying pre-pattern.

When the annealed block copolymer layer is subject to etching, thedifference in the etch rates between the two lamellar regions of theblock copolymer can be used to generate additional patterns when bothlamellar regions are exposed to the surface. In these instances, aportion of the block copolymer layer can be selectively removed toprovide a semiconductor device having a nano-scale pattern. Types ofetching include any common etching applied in the manufacture ofsemiconductor devices, for example, dry-etching such as plasma etching,or wet-etching using selective solvents. Typically, dry etchingprocesses are employed for etching at sub-50 nm dimensions.

Also disclosed are semiconductor devices manufactured using theabove-described method. In an embodiment, a semiconductor devicecomprises a substrate, the substrate comprising a topographicpre-pattern comprising a ridge surface separated by a height, h, greaterthan 0 nanometers from a trench surface; and a layer comprising a blockcopolymer disposed on the substrate, the block copolymer comprising twoor more block components, and the layer having a thickness of more than0 nanometers over the ridge surface and the trench surface; wherein thelayer comprises a block copolymer pattern having a periodicity of thetopographic pre-pattern, the block copolymer pattern comprisingmicrodomains of self-assembled block copolymer disposed on the ridgesurface and the trench surface, wherein the microdomains disposed on theridge surface have a different orientation compared to the microdomainsdisposed on the trench surface. In a another embodiment, themicrodomains of self-assembled block copolymer disposed on the ridgesurface and the trench surface of the semiconductor device have alamellar structure.

The above-described method permits a feature size less than 200 nm, moreparticularly less than 150 nm, and even more particularly less than 100nm. Secondly, the method advantageously replicates the periodicity ofthe underlying pre-pattern in the annealed block copolymer layer.

EXAMPLE

The following example demonstrates the method using a model blockcopolymer, poly(styrene-block-methyl methacrylate) (PS-b-PMMA).

(1) Preparation of Topographically Pre-Patterned Substrates:

Topographic pre-patterns were prepared by e-beam lithography followedplasma etching of silicon wafer. The depth of the pre-patterns iscontrolled as half of the period of lamellae (L₀). In this example,since the L₀ of PS-b-PMMA was approximately 40 nm, pre-patterns wereprepared having a height h (FIG. 1) of approximately 20 nm. The surfacefeatures of the pre-patterns had a variety of pitches (p) and widths(w).

(2) Block Copolymer Deposition:

The PS-b-PMMA had a number average molecular weight of 74.8 kg mol-1 (38kg mol⁻¹ for PS and 36.8 kg mol⁻¹ for PMMA), and thus an L₀ ofapproximately 37 nm. Thin films of PS-b-PMMA were spin-coated from 1.2wt % toluene solutions, based on total weight of the solution, onto thetopographic pre-patterns to form about 60 nm thick films (approximately1.5 L₀) after solvent removal.

(3) Thermal Annealing:

Subsequently the samples were annealed at 200° C. for 18 hours undernitrogen stream to induce the thermodynamically stable lamellarmorphology.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. The endpoints of all rangesdirected to the same characteristic or component are independentlycombinable and inclusive of the recited endpoint. In the description,all amounts, parts, ratios and percentages used herein are by weightunless otherwise specified.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method of forming a block copolymer pattern, comprising: providinga substrate comprising a topographic pre-pattern comprising a ridgesurface separated by a height, h, greater than 0 nanometers from atrench surface; disposing a block copolymer comprising two or more blockcomponents on the topographic pre-pattern to form a layer having athickness of more than 0 nanometers over the ridge surface and thetrench surface; and annealing the layer to form a block copolymerpattern having a periodicity of the topographic pre-pattern, the blockcopolymer pattern comprising microdomains of self-assembled blockcopolymer disposed on the ridge surface and the trench surface, whereinthe microdomains disposed on the ridge surface have a differentorientation compared to the microdomains disposed on the trench surface.2. The method of claim 1, wherein annealing forms microdomains ofself-assembled block copolymer having a lamellar structure disposed onthe ridge surface and the trench surface.
 3. The method of claim 2,wherein the microdomains having the lamellar structure disposed on theridge surface are oriented perpendicular to the ridge surface.
 4. Themethod of claim 2, wherein the microdomains having the lamellarstructure disposed on the trench surface are oriented parallel to thetrench surface.
 5. The method of claim 3, wherein the microdomainshaving the lamellar structure disposed on the ridge surface are alignedtransversely to a long axis of the ridge surface.
 6. The method of claim3, wherein the microdomains having the lamellar structure disposed onthe ridge surface are aligned parallel to a long axis of the ridgesurface.
 7. The method of claim 1, wherein the ridge surface has apreferential affinity for one of the two or more block components. 8.The method of claim 1, wherein the block copolymer has two blockcomponents.
 9. The method of claim 1, wherein the block copolymerpattern does not comprise a sphere or cylinder of one of the two or moreblock components in a matrix of a second block component.
 10. The methodof claim 1, wherein the block copolymer has asymmetric wettingcharacteristics; the block copolymer has a natural period of length, L₀;the layer has a thickness, t′, over the ridge surface that is less thanor equal to L₀; the layer has a thickness, t, over the trench surface,wherein t is less than t′; and the height, h, is at least 0.5L₀.
 11. Themethod of claim 1, wherein the block copolymer has symmetric wettingcharacteristics; the block copolymer has a natural period of length, L₀;the layer has a thickness, t′, over the ridge surface that is less thanor equal to 0.5L₀; the layer has a thickness, t, over the trenchsurface, wherein t′ is less than t; and the height, h, is at least0.5L₀.
 12. The method of claim 1, wherein the block copolymer has afirst polymeric block component A and a second polymeric block componentB, wherein a homopolymer of A is not miscible with a homopolymer of B.13. The method of claim 1, wherein annealing is by thermal treatment at200° C. to 300° C. for a time period of more than 0 hours to about 100hours.
 14. The method of claim 1, wherein the topographic pre-pattern isa line pattern, and the block copolymer pattern and the topographicpre-pattern have an identical pitch.
 15. The method of claim 1, whereinthe block copolymer comprises a polystyrene block component and apoly(meth)acrylate block component.
 16. The method of claim 1, furthercomprising etching the layer to selectively remove at least a portion ofthe block copolymer disposed on a trench surface.
 17. The method ofclaim 1, wherein the block copolymer comprises an A block component anda B block component, and a volume ratio of the A block component to theB block component is less than about 65:35 and is greater than about35:65.
 18. The method of claim 1, wherein the block copolymer comprisesan A block component and a B block component, and a volume ratio of theA block component to the B block component is less than about 80:20 andis greater than about 20:80.